Add minimal Kotlin DSL RouterFunction attributes support

Closes gh-28567

spring-webmvc/src/main/kotlin/org/springframework/web/servlet/function/RouterFunctionDsl.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -699,6 +699,30 @@ class RouterFunctionDsl internal constructor (private val init: (RouterFunctionD
 		builder.onError({it is E}, responseProvider)
 	}
 
+	/**
+	 * Add an attribute with the given name and value to the last route built with this builder.
+	 * @param name the attribute name
+	 * @param value the attribute value
+	 * @since 5.3
+	 */
+	fun withAttribute(name: String, value: Any) {
+		builder.withAttribute(name, value)
+	}
+
+	/**
+	 * Manipulate the attributes of the last route built with the given consumer.
+	 *
+	 * The map provided to the consumer is "live", so that the consumer can be used
+	 * to [overwrite][Map.put] existing attributes,
+	 * [remove][Map.remove] attributes, or use any of the other
+	 * [Map] methods.
+	 * @param attributesConsumer a function that consumes the attributes map
+	 * @since 5.3
+	 */
+	fun withAttributes(attributesConsumer: (MutableMap<String, Any>) -> Unit) {
+		builder.withAttributes(attributesConsumer)
+	}
+
 	/**
 	 * Return a composed routing function created from all the registered routes.
 	 */